Floor minor fault activation-seepage stability loss modeling method under mining influence

Abstract

The invention relates to a floor minor fault activation-seepage loss stability modeling method under mining influence. The method comprises the following steps: S1, constructing a minor fault failure unit mechanical model; s2, constructing a minor fault slip instability model; and S3, constructing a small fault seepage stability loss model. The mechanical model is constructed by adopting a theoretical analysis method, the damage process of the floor and the seepage water inrush phenomenon are clarified, and a theoretical basis is provided for revealing a working face minor fault floor lagging water inrush mechanism.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology, specifically relating to a modeling method for the activation-seepage instability of small faults in the floor under mining influence. Background Technology

[0002] With the increasing depth of coal mining, the threat posed by high-pressure water and strong mining stress in the complex geological environment of "high pressure, high temperature, high humidity, and high disturbance" to the safe mining of coal seams is becoming increasingly prominent. Engineering practice shows that even if a large number of mines strictly follow the current technical specifications for water prevention and control, they still frequently experience delayed water inrush disasters induced by small faults in the longwall mining face.

[0003] Mining-induced activation of small faults is one of the main causes of floor water inrush in mines. Due to their characteristics such as strong concealment, fractured interstitial material, poor tensile and shear strength, and well-developed joints, these factors collectively reduce the integrity of the floor strata and the thickness of the aquitard, thereby increasing the likelihood of floor water inrush before and after the working face passes over the fault. This risk is further exacerbated by various factors, including coal seam depth, mining thickness, mining method, water pressure in the floor aquifer, distance between the coal seam and the aquifer, fault orientation, and the characteristics of the interstitial material. The delayed water inrush phenomenon that occurs after the working face pushes over the fault in a confined aquifer is mainly due to the fact that this type of small fault is a closed non-conductive fault with low porosity. Under the action of a single water pressure, it is not enough to cause the structural instability and water inrush of the small fault in the bottom plate. However, after the small fault is affected by mining activities, it will cause the upper and lower walls to slide and shift, resulting in structural instability. High-pressure water seeps upward and eventually causes seepage instability, causing water inrush events in the goaf behind the working face. When the disturbance stress caused by mining reaches a sufficient intensity, it will cause damage and sliding of the small fault and the surrounding rock.

[0004] Therefore, there is an urgent need for a modeling method for the activation-seepage instability of small faults in the foundation under the influence of mining, in order to deal with the dual characteristics of small faults as "static water-blocking and dynamic water-conducting", and to provide a guarantee for the safe mining of deep resources. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, this application employs theoretical analysis to construct a mechanical model, clarifying the damage and failure process of the floor slab and the seepage and water inrush phenomenon, thus providing a theoretical basis for revealing the delayed water inrush mechanism of the floor slab in small faults at the working face. This invention provides a modeling method for the activation-seepage destabilization of small faults in the floor slab under mining influence. The modeling method includes the following steps: Step S1, constructing a mechanical model of a small fault failure element, including: Step S1-1: Obtain the upper stress q of the mechanical model of the small fault failure element. x ; Step S1-2: Obtain the stress components at each point in the mechanical model of the small fault failure unit; Step S1-3: Obtain the difference between the shear stress on the slip fault and the shear stress on the fault plane: Δτ; The condition for a small fault to undergo slip failure is Δτ>0; Step S2, construct a small fault slip instability model, including: Step S2-1: Perform stress analysis on the inclined sections of the hanging wall and footwall of the small fault; Step S2-2: Perform stress analysis on the hanging wall and footwall of the small fault; Step S2-3: Obtain the frictional forces of the hanging wall and footwall of the small fault; Step S2-4: Obtain the advance support force and the stress behind the working face; Step S2-5: Perform force synthesis on the inclined plane of the small fault. Step S2-6: Obtain the activation conditions for small faults; Step S3, construct a seepage instability model for small faults, including: Step S3-1: Obtain the normal stress relief model; Step S3-2: Obtain the formula for calculating fracture permeability; Step S3-3: Obtain the seepage equation to get the expected water inrush volume of the small fault in the bottom plate.

[0006] Preferably, in step S1-1, the stress q in the upper part of the mechanical model of the small fault failure element is... x As shown in the following formula: ; In the formula: q is the water pressure of the bottom aquifer, in MPa; K is the pressure concentration coefficient of the working face advance support; H is the thickness of the bottom aquifer, in m; γ is the average unit weight of the overlying strata on the working face, in kN / m³; a is the distance from the fault to the cut hole, in m; L is the working face advance distance, in m.

[0007] Preferably, in step S1-2, the stress components at each point within the mechanical model of the small fault failure unit are as shown in the following equation: ; In the formula: h is the distance from the bottom of the coal seam to the top interface of the aquifer; σ x σ represents the stress component in the x-direction, in MPa. y τ represents the stress component in the y-direction, in MPa. xy : shear force in the x and y directions, in MPa; q: water pressure in the aquifer at the bottom plate, in MPa; x: x-coordinate parameter of any point in the model, in meters; y: y-coordinate parameter of any point in the model, in meters; L: distance the working face pushes across the small fault, in meters.

[0008] Preferably, steps S1-3 include: Step S1-3-1: The angle between any element of the small fault in the base plate and the fault scratch is α. According to the coordinate rotation transformation formula, the shear stress τ and normal stress σ on the fault are obtained. n As shown in the following formula: ; ; Step S1-3-2: Based on soil mechanics theory, obtain the shear strength τ of the fault plane. s As shown in the following formula: ; In the formula: C is the cohesion of the small fault, in MPa; ψ is the internal friction angle, in °; Step S1-3-3, will and Subtracting the values ​​yields Δτ. The condition for slip failure in a small fault is Δτ > 0, as shown in the following equation: ; Among them, the maximum principal stress of a certain unit within the water-resistant small fault zone is σ1, and the minimum principal stress is σ3.

[0009] Preferably, step S2-2 involves performing a stress analysis on the hanging wall of the small fault, including: ; ; Stress analysis of the footwall of the small fault, including: ; ; In the formula: F N1 F represents the bearing pressure on the hanging wall strata of a small fault, expressed in kN. N2 F1 is the bearing pressure on the footwall strata of the small fault, in kN; F2 is the sum of vertical forces on the hanging wall of the small fault excluding the self-weight of the rock mass, in kN; F1(x), F2(x), and F3(x) are all loads on the upper part of the aquitard layer of the bottom plate, F2(x) = q1, kN / m; P(x) is the average water pressure on the aquitard layer of the bottom plate, in kN / m; γ is the average unit weight of the overlying strata on the working surface, in kN / m. 3 H represents the thickness of the waterproof layer on the base plate, in meters; l c l1 represents the action length of F1(x) on the hanging wall of the small fault, in meters; l2 represents the action length of F2(x) on the hanging wall of the small fault, in meters; l d The length of action of P(x) on the hanging wall of the small fault, in meters; l bThe length of action of P(x) on the footwall of the small fault, in meters; l x The effective length of F2(x) on the floor of the goaf, in meters; l a The length of the hanging wall of the small fault is in meters. Step S2-3: Obtain the frictional force F between the hanging wall and footwall of the small fault. N As shown in the following formula: .

[0010] Preferably, in step S2-4, the leading support force f1(x) and the rear stress f2(x) of the working face are obtained, as shown in the following formula; ; ; ; Wherein, τ0 is the ultimate shear strength of the coal seam, in MPa; ψ1 is the internal friction angle of the coal seam in °; f is the friction factor between the coal seam and the roof; M is the coal seam thickness, in m; K is the concentration factor of the advance support pressure of the working face; and γ is the average unit weight of the overlying strata on the working face, in kN / m³. 3 H is the thickness of the bottom waterproof layer, in meters; β is the stress concentration factor; x is the distance from any position on the bottom plate of the working face to the boundary of the model, in meters; L1 is the horizontal distance from the working face to the peak of the support pressure, in meters; L2 is the horizontal distance from the peak of the support pressure to the starting point of the original rock stress, in meters; L3 is the distance from the starting point of the original rock stress to the stop line of the working face, in meters. Steps S2-5 involve force synthesis on the inclined plane of the small fault, including: Assume the lateral stress T on the working surface is as follows: ; Where H is the thickness of the bottom slab's waterproof layer, in meters; q is the water pressure of the bottom slab's aquifer, in MPa. Force synthesis is performed on the slope of a small fault, including: ; ; The final result is: as well as expression; Among them, F x F represents the resultant force in the x-direction at the small fault, in kN. y F represents the resultant force in the y-direction at the small fault, in kN. N2 F represents the bearing pressure on the footwall strata of a small fault, expressed in kN. N1T1 is the bearing pressure on the hanging wall strata of the small fault, in kN; T2 is the cohesive force on the footwall of the small fault, in kN; T1 is the cohesive force on the hanging wall of the small fault, in kN; θ is the dip angle of the small fault, in °; H is the thickness of the aquitard layer on the bottom plate, in m; q2 is the lateral load on the small fault model, in kN. Steps S2-6: Obtain the activation conditions for small faults; slippage requires shear force greater than the maximum static friction force, i.e. ( ); θ is the dip angle of the minor fault, in °; The friction angle within the rock mass is expressed in °. The activation conditions for fault formation can be obtained as shown in the following formula: .

[0011] Preferably, in step S3-1, the normal stress relief model is obtained. As shown in the following formula: ; In the formula: α is the normal stress of the original rock, in MPa; α is the stress attenuation coefficient, in m. -1 L represents the working face advance distance in meters; L1 represents the distance from the cut to the small fault in meters. The original rock normal stress is: ; The shear stress near the goaf is: ; in, ; The shear stress accompanying the advancement of the working face is expressed in MPa. β is the initial shear stress, MPa; β is the stress concentration factor; L P The range of stress disturbance is 0.2H to 0.5H; θ is the dip angle of the small fault, in degrees.

[0012] Preferably, to characterize the floor damage caused by stress changes during mining, a damage variable D(L) is introduced to characterize the degree of fracture development: ; In the formula: D0 is the initial damage variable; α D γ is the damage coefficient; m is the stress sensitivity index; γ is the attenuation coefficient; Damage variables are related to effective shear stress and propulsion distance: ; ; In the formula: C is the cohesion within the small fault, in MPa; P w The pressure of the pressurized water in the base plate is expressed in MPa. The shear stress at position L is expressed in MPa. The initial shear stress is expressed in MPa. Shear stress accompanying the advancement of the working face, in MPa; The normal stress at position L is expressed in MPa. The pressure of the pressurized water in the base plate is expressed in MPa.

[0013] Preferably, in step S3-2, the formula for calculating fracture permeability is as follows: ; ; ; Where: K f (L) represents the fracture permeability of the fracture zone in small faults at different advance distances; K f0 n represents the initial fracture permeability of the small fault fracture zone. f (L) represents the porosity of the fractured zone of the small fault at different advance distances; n f0 β is the initial porosity of the fault fracture zone; f is the stress concentration factor; D is the friction factor between the coal seam and the roof. (L) represents the damage variable; γ represents the average unit weight of the overburden strata on the working surface, kN / m³. 3 ;n fmaxf This represents the maximum porosity of the small fault fracture zone.

[0014] Preferably, considering only the location between the working face and the small fault and the aquifer water pressure, step S3-3 yields the seepage equation as shown below: ; The boundary condition for the seepage equation is that the water pressure in the goaf is P(L) = P0 ≈ 0, where the confined aquifer water pressure in the small fault is P(L1) = P w ; Integrating the above equation yields the water pressure gradient: ; The estimated water inrush volume at the small fault in the base plate is shown in the following formula: ; In the formula: K(L) represents the permeability of the fracture zone in the bottom plate at different advance distances; P0 is the water pressure of the confined water in the base plate, in MPa; L1 is the water pressure in the goaf, in MPa; L2 is the working face advance distance, in m; L3 is the distance from the cut-in hole to the small fault, in m; A is the area of ​​the water diversion channel, in m². 2 b is the width of the water diversion channel, in meters; h is the distance from the bottom of the coal seam to the top interface of the aquifer.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: Analyzing the main controlling factors of delayed water inrush at the floor of a small fault in a working face is a complex and multifaceted problem, involving multiple fields such as geology, mining engineering, and hydrogeology. The main controlling factors include fault characteristics, mine pressure, aquitard thickness, working face width, groundwater pressure, heterogeneity of fault infill material, and the influence of mining-induced stress. In practical work, these factors need to be comprehensively considered, and corresponding prevention and control measures need to be taken to reduce the risk of delayed water inrush.

[0016] This application constructs a mechanical model for small fault activation and a model for small fault damage and seepage stability, considering the coupling of multiple factors such as mining effects, bottom aquitard thickness, and aquifer water pressure. The structural characteristics of the wellbore in small faults have a significant impact on their stability. The higher the density of the fracture zone and the smaller the internal friction angle, the stronger its resistance to slippage. The dip angle of small faults is negatively correlated with the ease of activation. A decrease in the dip angle of small faults leads to an enhancement of the static friction effect on the fault surface, significantly increasing the slippage activation threshold. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the mechanical model of the fault scratch unit of the small fault involved in the present invention; Figure 2 This is a schematic diagram illustrating the stress analysis of the inclined sections of the hanging wall and footwall of a small fault, as per the present invention. Figure 3 This is a schematic diagram of a load-bearing model of the top of the hanging wall of a small fault, as per the present invention. Detailed Implementation

[0018] To better understand this invention, the following description, in conjunction with the accompanying drawings and examples, will further illustrate the invention.

[0019] An improved modeling method for the activation-seepage destabilization of small faults in the foundation under mining influence, the method includes the following steps: Step S1, constructing a mechanical model of a small fault failure element, including: Step S1-1: Obtain the upper stress q of the mechanical model of the small fault failure element. x .

[0020] Step S1-2: Obtain the stress components at each point in the mechanical model of the small fault failure unit; Step S1-3: Obtain the difference between the shear stress on the fault and the shear stress on the fault plane: Δτ; The condition for a small fault to undergo slip failure is Δτ>0.

[0021] Specifically, based on the concept of a water-retaining critical layer and the analysis of the impact of mining disturbance on the small faults in the floor, the structural mechanical model of the water-retaining critical layer can be simplified into a rectangular thin plate with various boundary conditions. Before mining disturbance, the interface from the coal seam floor to the top of the aquifer can be regarded as the water-retaining critical layer. The stress dynamics of the floor change before and after the working face pushes past the small fault, and its stress boundary conditions change dynamically accordingly. Step S1-1, considering the mining geology and hydrogeology conditions of the working face, after the impact of mining, the stress q in the upper part of the mechanical model of the small fault failure unit... x As shown in the following formula: (1-1) In the formula: q is the water pressure of the bottom aquifer, MPa; K is the pressure concentration coefficient of the working face advance support; H is the thickness of the bottom aquifer, m; γ is the average unit weight of the overlying strata on the working face, kN / m³; a is the distance from the fault to the cut hole, m; L is the working face advance distance, m.

[0022] Step S1-2, based on the theory of elasticity, yields the stress components at each point within the model, as shown in the following formula. This formula is mainly used to calculate the stress at each point within the model, providing a theoretical basis for the subsequent establishment of a mechanical model of a small fault slip-scratch unit.

[0023] (1-2) In the formula: h is the distance from the bottom of the coal seam to the top interface of the aquifer; σ x σ represents the stress component in the x-direction, in MPa. y τ represents the stress component in the y-direction, in MPa. xy : shear force in the x and y directions, in MPa; q: water pressure in the aquifer at the bottom plate, in MPa; x: x-coordinate parameter of any point in the model, in meters; y: y-coordinate parameter of any point in the model, in meters; L: distance the working face pushes across the small fault, in meters.

[0024] From formula (1-2), the maximum principal stress of a certain element within the water-resistant small fault zone can be obtained as σ1, and the minimum principal stress as σ3. Thus, a mechanical model of the fault's slip-scratch element can be established, such as... Figure 1 As shown.

[0025] Step S1-3, obtain the difference Δτ between the shear stress on the fault and the shear stress on the fault plane, including: Step S1-3-1: The angle between any element of the small fault in the base plate and the fault scratch is α. According to the coordinate rotation transformation formula, the shear stress and normal stress on the fault can be obtained, as shown in formulas (1-3) and (1-4).

[0026] (1-3) (1-4) Step S1-3-2: Small faults have strong water-impermeability, and the fault fracture zone can be assumed to be in an unsaturated water state. Without considering water pressure, according to soil mechanics theory, the shear strength of the fault plane can be obtained as follows: (1-5) In the formula: C is the cohesion of the small fault, MPa; φ is the internal friction angle, °.

[0027] Step S1-3-3, subtract equation (1-3) from equation (1-5) to obtain Δτ: (1-6) The condition for slip failure of a small fault is Δτ>0; where the maximum principal stress of a certain element in the water-resistant small fault zone is σ1 and the minimum principal stress is σ3.

[0028] Step S2: Construct a small fault slip instability model.

[0029] The fundamental reason for delayed water inrush induced by small faults is the activation of damage caused by mining stress. Structurally, this activation is caused by the slippage of the hanging wall and footwall of the small fault. Based on mining geological conditions, the model can be generalized, and a mechanical model of small fault damage activation considering factors such as mining effects, the thickness of the floor aquitard, and aquifer water pressure is established. See details. Figure 2 .

[0030] Analysis of forces on small faults includes: Step S2-1: Perform stress analysis on the inclined sections of the hanging wall and footwall of the small fault, as follows: Figure 2 As shown, F N From the force composition along the small fault, we can see that: (2-1) In the formula: F N T is the supporting pressure of the small fault on the upper part, kN; T is the horizontal compressive force of the small fault on the right end, kN; θ is the dip angle of the small fault, (°); F x F y These are the resultant forces in the x and y directions at the small fault, respectively, in kN.

[0031] For a small fault to cause slippage between its hanging wall and footwall, the shear force must be greater than the maximum static friction force. (2-2) In the formula: φ is the internal friction angle of the rock mass in the fracture zone of the small fault.

[0032] From equation (2-1), we can see that The principle of constant stability means that the contact between the hanging wall and footwall of a small fault will not result in non-contact delamination due to mining.

[0033] Combining equations (2-1) and (2-2), we obtain: (2-3) Step S2-2 yields the stress on the hanging wall of the small fault, as shown in formulas (2-4) and (2-5); and the stress on the footwall of the small fault, as shown in formulas (2-6) and (2-7). Based on the mining conditions, the stress analysis of the hanging wall and footwall of the small fault reveals the following: Hanging wall of the fault: (2-4) (2-5) Footwall of the fault: (2-6) (2-7) In the formula: F N1 F N2 F1 and F2 are the supporting pressures on the hanging and footwall strata of the small fault, respectively, in kN; F1 and F2 are the sum of the vertical forces on the hanging and footwall strata of the small fault excluding the self-weight of the rock mass, respectively, in kN; P(x) is the average water pressure on the bottom aquitard, in kN / m; F1(x), F2(x), and F3(x) are the loads on the upper part of the bottom aquitard, F2(x) = q1, in kN / m; γ is the average unit weight of the overlying strata on the working surface, in kN / m. 3 H is the thickness of the bottom waterproof layer, in meters; l0 is the length of the F2(x) action on the hanging wall of the small fault, in meters; l x The effective length of F2(x) in the goaf floor is given in meters (m). a The length of the hanging wall of the small fault is in meters (m); l b The length of action of P(x) on the footwall of the small fault, in meters; l c The length of action of F1(x) on the hanging wall of the small fault, in meters; l d Let P(x) be the length of action of the hanging wall of the small fault, in meters.

[0034] Step S2-3, integrating the above equation, yields the frictional forces on the hanging wall and footwall of the small fault: (2-8) In the formula: M is the coal seam thickness, m; f is the friction factor between the coal seam and the roof, generally 0.01~0.03; φ1 is the internal friction angle of the coal seam, °; K is the working face advance support pressure concentration factor; τ0 is the ultimate shear strength of the coal body, MPa; β is the coal seam lateral pressure coefficient, generally 0.8~1.5.

[0035] Before the working face pushes past the small fault, the fault will not undergo slip activation. As the working face moves further away, the stress on the footwall of the small fault gradually changes. Based on the distribution law of the advance support pressure, assuming F1(x) = F3(x), a load model of the top of the hanging wall of the small fault is established as follows: Figure 3 As shown.

[0036] Step S2-4, obtain the leading support force f1(x) and the rear stress f2(x) of the working face as follows: (2-9) (2-10) (2-11) Wherein, τ0 is the ultimate shear strength of the coal seam, in MPa; ψ1 is the internal friction angle of the coal seam in °; f is the friction factor between the coal seam and the roof; M is the coal seam thickness, in m; K is the concentration factor of the advance support pressure of the working face; and γ is the average unit weight of the overlying strata on the working face, in kN / m³. 3 H is the thickness of the bottom plate waterproof layer, in meters; β is the stress concentration factor; x is the distance from any position on the bottom plate of the working face to the boundary of the model, in meters; L1 is the horizontal distance from the working face to the peak of the support pressure, in meters; L2 is the horizontal distance from the peak of the support pressure to the starting point of the original rock stress, in meters; L3 is the distance from the starting point of the original rock stress to the stop line of the working face, in meters.

[0037] Step S2-5, assuming the lateral stress on the working surface is: (2-12) Where H is the thickness of the bottom slab's waterproof layer, in meters; q is the water pressure of the bottom slab's aquifer, in MPa. Force composition is performed on the inclined plane of a small fault: (2-13) (2-14) (2-15) (2-16) Among them, F x F represents the resultant force in the x-direction at the small fault, in kN. y F represents the resultant force in the y-direction at the small fault, in kN. N2 F represents the bearing pressure on the footwall strata of a small fault, expressed in kN. N1T1 is the bearing pressure on the hanging wall strata of the small fault, in kN; T2 is the cohesive force on the footwall of the small fault, in kN; T1 is the cohesive force on the hanging wall of the small fault, in kN; θ is the dip angle of the small fault, in °; H is the thickness of the aquitard layer on the bottom plate, in m; q2 is the lateral load on the small fault model, in kN.

[0038] Steps S2-6 require that the shear force be greater than the maximum static friction force to generate slip, i.e. ( ); θ is the dip angle of the minor fault, in °; denoted as the friction angle within the rock mass, in °.

[0039] The activation conditions for fault formation can be determined as follows: (2-17) Right now: (2-18) (2-19) Combining the above equations, we can obtain the activation conditions for small faults: (2-20) According to the formula for the activation of small faults, under certain conditions, the denser and more stable the structure of the small fault itself, the smaller its internal friction angle, and the less likely it is to slip or slide. The smaller the dip angle of the small fault, the greater the static friction required for activation, and the less likely it is to slip or slide. Furthermore, the activation of small faults is related to the coal seam depth, the thickness of the floor aquitard, the aquifer water pressure, the working face advance distance, and the coal seam thickness. The deeper the coal seam, the thinner the floor aquitard, the higher the aquifer water pressure, and the thicker the coal seam, the easier it is for activation to occur.

[0040] Step S3: Construct a small fault seepage instability model.

[0041] Small fault activation, a crucial link in geodynamic processes, is typically predicated on slip instability. Therefore, based on a thorough analysis of small fault slip instability models, a damage-seepage instability model for small faults needs to be constructed. First, a spatial stress model is established to express the changes in normal and tangential stresses with the advancing face. To describe the damage caused by stress release in the base plate and changes in spatial distance as the working face advances, an evolution equation for the damage variable D(L) is defined, the relationship between porosity and permeability is derived, a seepage equation is established to solve for water pressure distribution and inrush flow rate, and an inrush flow rate threshold is used to formulate an inrush criterion.

[0042] Before establishing a seepage instability model for small faults, it is necessary to first establish a spatial stress distribution model after the working face pushes past the small fault. By analyzing the changes in normal stress and shear stress, the stress field near the small fault and surrounding rock at different working face advance distances can be obtained.

[0043] As the working face advances, the unloading of the goaf causes the normal stress on the small fault to decrease with distance. Step S3-1, obtain the normal stress release model, as shown in equation (3-1): (3-1) In the formula: α is the original rock normal stress, MPa; α is the stress attenuation coefficient, m -1 L is the working face advance distance, in meters; L1 is the distance from the cut to the small fault, in meters. The original rock normal stress is: (3-2) As the working face advances, the shear stress near the goaf increases with the advancing distance L: (3-3) (3-4) In the formula: The shear stress accompanying the advancement of the working face is expressed in MPa. β is the initial shear stress, MPa; β is the stress concentration factor; L P The range of stress disturbance is 0.2H to 0.5H.

[0044] To characterize the floor failure caused by stress changes during mining, a damage variable D(L) is introduced to characterize the degree of fracture development: (3-5) In the formula: D0 is the initial damage variable (D0=0 indicates no damage); α D γ is the damage coefficient; m is the stress sensitivity index; γ is the attenuation coefficient.

[0045] Damage variables are related to effective shear stress and propulsion distance.

[0046] (3-6) (3-7) In the formula: C is the cohesion within the small fault, MPa; P w The pressure of the pressurized water in the base plate is measured in MPa. The shear stress at position L is expressed in MPa. The initial shear stress is expressed in MPa. Shear stress accompanying the advancement of the working face, in MPa; The normal stress at position L is expressed in MPa. The pressure of the pressurized water in the base plate is expressed in MPa.

[0047] The small fault in the base plate is affected by mining stress and aquifer water pressure, which will change the internal pore and fracture structure of the fracture zone. Pores and fractures can be divided into two categories: matrix pores and fractures between blocks. The change in permeability of matrix pores under stress is much smaller than that of fractures. Therefore, we only consider the change in fracture permeability caused by damage in the fracture zone of the small fault, and the change in fracture permeability is controlled by the degree of damage. Step S3-2, the fracture permeability calculation formula is as follows: (3-8) (3-9) (3-10) Where: K f (L) represents the fracture permeability of the fracture zone in small faults at different advance distances; K f0 n represents the initial fracture permeability of the small fault fracture zone. f (L) represents the porosity of the fractured zone of the small fault at different advance distances; n f0 β is the initial porosity of the fault fracture zone; f is the stress concentration factor; D is the friction factor between the coal seam and the roof. (L) represents the damage variable; γ represents the average unit weight of the overburden strata on the working surface, kN / m³. 3 ;n fmaxf This represents the maximum porosity of the small fault fracture zone.

[0048] Considering only the location between the working face and the small fault and the aquifer water pressure, step S3-3 yields the seepage equation as follows: (3-11) The boundary condition for this seepage equation is that the water pressure in the goaf is P(L) = P0 ≈ 0, where the confined water pressure in the small fault is P(L1) = P w .

[0049] Integrating the above equation yields the water pressure gradient: (3-12) The estimated water inrush volume at the small fault in the base plate is: (3-13) In the formula: K(L) represents the permeability of the fracture zone in the bottom plate at different advance distances; P0 is the water pressure of the confined water in the base plate, in MPa; L1 is the water pressure in the goaf, in MPa; L2 is the working face advance distance, in m; L3 is the distance from the cut-in hole to the small fault, in m; A is the area of ​​the water diversion channel, in m². 2 b is the width of the water diversion channel, in meters; h is the distance from the bottom of the coal seam to the top interface of the aquifer.

[0050] Water inrush at the coal mine working face floor is a significant type of mine water hazard. Its classification and judgment criteria primarily rely on the inrush volume, characteristics, and severity. Based on the inrush volume, floor inrushes are typically classified into the following levels: small inrush (10 m³ / h ≤ Q < 50 m³ / h), medium inrush (50 m³ / h ≤ Q < 150 m³ / h), large inrush (150 m³ / h ≤ Q < 600 m³ / h), and extremely large inrush (Q ≥ 600 m³ / h). Due to the limitations of small fault water-conducting channels, the likelihood of large and extremely large inrushes is relatively low; therefore, small and medium inrushes are sufficient as criteria. When the predicted inrush volume indicates a small inrush, if the drainage capacity exceeds the inrush volume, pumping can be carried out according to the actual situation, or local grouting can be performed to reduce the permeability of the fractured zone of the small fault. When the predicted inrush volume indicates a medium inrush, high-pressure grouting is required to seal the entire fractured zone of the small fault.

[0051] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0052] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0053] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0054] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0055] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.

Claims

1. A method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence, characterized in that, The modeling method includes the following steps: Step S1, constructing a mechanical model of a small fault failure element, including: Step S1-1: Obtain the upper stress q of the mechanical model of the small fault failure element. x ; Step S1-2: Obtain the stress components at each point in the mechanical model of the small fault failure unit; Step S1-3: Obtain the difference between the shear stress on the slip fault and the shear stress on the fault plane: Δτ; The condition for a small fault to undergo slip failure is Δτ>0; Step S2, construct a small fault slip instability model, including: Step S2-1: Perform stress analysis on the inclined sections of the hanging wall and footwall of the small fault; Step S2-2: Perform stress analysis on the hanging wall and footwall of the small fault; Step S2-3: Obtain the frictional forces of the hanging wall and footwall of the small fault; Step S2-4: Obtain the advance support force and the stress behind the working face; Step S2-5: Perform force synthesis on the inclined plane of the small fault. Step S2-6: Obtain the activation conditions for small faults; Step S3, construct a seepage instability model for small faults, including: Step S3-1: Obtain the normal stress relief model; Step S3-2: Obtain the formula for calculating fracture permeability; Step S3-3: Obtain the seepage equation to get the expected water inrush volume of the small fault in the bottom plate.

2. The method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence as described in claim 1, characterized in that, Step S1-1, upper stress q of the mechanical model of the small fault failure element x As shown in the following formula: ； In the formula: q is the water pressure of the bottom aquifer, in MPa; K is the pressure concentration coefficient of the working face advance support; H is the thickness of the bottom aquifer, in m; γ is the average unit weight of the overlying strata on the working face, in kN / m³; a is the distance from the fault to the cut hole, in m; L is the working face advance distance, in m.

3. The method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence as described in claim 1, characterized in that, Step S1-2, the stress components at each point in the mechanical model of the small fault failure element are shown in the following equation: ； In the formula: h is the distance from the bottom of the coal seam to the top interface of the aquifer; σ x σ represents the stress component in the x-direction, in MPa. y τ represents the stress component in the y-direction, in MPa. xy : shear force in the x and y directions, in MPa; q: water pressure in the aquifer at the bottom plate, in MPa; x: x-coordinate parameter of any point in the model, in meters; y: y-coordinate parameter of any point in the model, in meters; L: distance the working face pushes across the small fault, in meters.

4. The method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence as described in claim 1, characterized in that, Steps S1-3 include: Step S1-3-1: The angle between any element of the small fault in the base plate and the fault scratch is α. According to the coordinate rotation transformation formula, the shear stress τ and normal stress σ on the fault are obtained. n As shown in the following formula: ； ； Step S1-3-2: Based on soil mechanics theory, obtain the shear strength τ of the fault plane. s As shown in the following formula: ； In the formula: C is the cohesion of the small fault, in MPa; ψ is the internal friction angle, in °; Step S1-3-3, will and Subtracting the values ​​yields Δτ. The condition for slip failure in a small fault is Δτ > 0, as shown in the following equation: ； Among them, the maximum principal stress of a certain unit within the water-resistant small fault zone is σ1, and the minimum principal stress is σ3.

5. The method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence as described in claim 1, characterized in that, Step S2-2 involves performing a stress analysis on the hanging wall of the small fault, including: ； ； Stress analysis of the footwall of the small fault, including: ； ； In the formula: F N1 F represents the bearing pressure on the hanging wall strata of a small fault, expressed in kN. N2 F1 is the bearing pressure on the footwall strata of the small fault, in kN; F2 is the sum of vertical forces on the hanging wall of the small fault excluding the self-weight of the rock mass, in kN; F1(x), F2(x), and F3(x) are all loads on the upper part of the aquitard layer of the bottom plate, F2(x) = q1, kN / m; P(x) is the average water pressure on the aquitard layer of the bottom plate, in kN / m; γ is the average unit weight of the overlying strata on the working surface, in kN / m. 3 H represents the thickness of the waterproof layer on the base plate, in meters; l c l1 represents the action length of F1(x) on the hanging wall of the small fault, in meters; l2 represents the action length of F2(x) on the hanging wall of the small fault, in meters; l d The length of action of P(x) on the hanging wall of the small fault, in meters; l b The length of action of P(x) on the footwall of the small fault, in meters; l x The effective length of F2(x) on the floor of the goaf, in meters; l a The length of the hanging wall of the small fault is in meters. Step S2-3: Obtain the frictional force F between the hanging wall and footwall of the small fault. N As shown in the following formula: 。 6. The method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence as described in claim 5, characterized in that, Step S2-4: Obtain the leading support force f1(x) and the rear stress f2(x) of the working face, as shown in the following formula; ； ； ； Wherein, τ0 is the ultimate shear strength of the coal seam, in MPa; ψ1 is the internal friction angle of the coal seam in °; f is the friction factor between the coal seam and the roof; M is the coal seam thickness, in m; K is the concentration factor of the advance support pressure of the working face; and γ is the average unit weight of the overlying strata on the working face, in kN / m³. 3 H is the thickness of the bottom waterproof layer, in meters; β is the stress concentration factor; x is the distance from any position on the bottom plate of the working face to the boundary of the model, in meters; L1 is the horizontal distance from the working face to the peak of the support pressure, in meters; L2 is the horizontal distance from the peak of the support pressure to the starting point of the original rock stress, in meters; L3 is the distance from the starting point of the original rock stress to the stop line of the working face, in meters. Steps S2-5 involve force synthesis on the inclined plane of the small fault, including: Assume the lateral stress T on the working surface is as follows: ； Where H is the thickness of the bottom slab's waterproof layer, in meters; q is the water pressure of the bottom slab's aquifer, in MPa. Force synthesis is performed on the slope of a small fault, including: ； ； The final result is: as well as expression; Among them, F x F represents the resultant force in the x-direction at the small fault, in kN. y F represents the resultant force in the y-direction at the small fault, in kN. N2 F represents the bearing pressure on the footwall strata of a small fault, expressed in kN. N1 T1 is the bearing pressure on the hanging wall strata of the small fault, in kN; T2 is the cohesive force on the footwall of the small fault, in kN; T1 is the cohesive force on the hanging wall of the small fault, in kN; θ is the dip angle of the small fault, in °; H is the thickness of the aquitard layer on the bottom plate, in m; q2 is the lateral load on the small fault model, in kN. Steps S2-6: Obtain the activation conditions for small faults; slippage requires shear force greater than the maximum static friction force, i.e. ( ); θ is the dip angle of the minor fault, in °; The friction angle within the rock mass is expressed in °. The activation conditions for fault formation can be obtained as shown in the following formula: 。 7. The method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence as described in claim 1, characterized in that, Step S3-1: Obtain the normal stress relief model As shown in the following formula: ； In the formula: α is the normal stress of the original rock, in MPa; α is the stress attenuation coefficient, in m. -1 L represents the working face advance distance in meters; L1 represents the distance from the cut to the small fault in meters. The original rock normal stress is: ; The shear stress near the goaf is: ; in, ; The shear stress accompanying the advancement of the working face is expressed in MPa. β is the initial shear stress, MPa; β is the stress concentration factor; L P The range of stress disturbance is 0.2H to 0.5H; θ is the dip angle of the small fault, in degrees.

8. The method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence as described in claim 7, characterized in that, To characterize the floor failure caused by stress changes during mining, a damage variable D(L) is introduced to characterize the degree of fracture development: ； In the formula: D0 is the initial damage variable; α D γ is the damage coefficient; m is the stress sensitivity index; γ is the attenuation coefficient; Damage variables are related to effective shear stress and propulsion distance: ； ； In the formula: C is the cohesion within the small fault, in MPa; P w The pressure of the pressurized water in the base plate is expressed in MPa. The shear stress at position L is expressed in MPa. The initial shear stress is expressed in MPa. Shear stress accompanying the advancement of the working face, in MPa; The normal stress at position L is expressed in MPa. The pressure of the pressurized water in the base plate is expressed in MPa.

9. The method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence as described in claim 1, characterized in that, Step S3-2, obtain the following formula for calculating fracture permeability: ； ； ； Where: K f (L) represents the fracture permeability of the fracture zone in small faults at different advance distances; K f0 n represents the initial fracture permeability of the small fault fracture zone. f (L) represents the porosity of the fractured zone of the small fault at different advance distances; n f0 β is the initial porosity of the fault fracture zone; f is the stress concentration factor; D(L) is the friction factor between the coal seam and the roof; γ is the damage variable; and γ is the average unit weight of the overburden strata on the working face (kN / m³). 3 ;n fmaxf This represents the maximum porosity of the small fault fracture zone.

10. The method for modeling the activation-seepage instability of small faults in the foundation plate under mining influence as described in claim 1, characterized in that, Considering only the location between the working face and the small fault and the aquifer water pressure, step S3-3 yields the seepage equation as shown below: ； The boundary condition for the seepage equation is that the water pressure in the goaf is P(L) = P0 ≈ 0, where the confined aquifer water pressure in the small fault is P(L1) = P w ; Integrating the above equation yields the water pressure gradient: ； The estimated water inrush volume at the small fault in the base plate is shown in the following formula: ； In the formula: K(L) represents the permeability of the fracture zone in the bottom plate at different advance distances; P0 is the water pressure of the confined water in the base plate, in MPa; L1 is the water pressure in the goaf, in MPa; L2 is the working face advance distance, in m; L3 is the distance from the cut-in hole to the small fault, in m; A is the area of ​​the water diversion channel, in m². 2 b is the width of the water diversion channel, in meters; h is the distance from the bottom of the coal seam to the top interface of the aquifer.

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